1. Field of the Invention
The present invention relates to a method for boring a bicycle wheel spoke rim. The invention also relates to a bicycle rim obtained using the method.
2. Background and Material Information
In a known manner, a wheel, especially a bicycle wheel, includes a central hub connected to a circular rim by two rows of spokes. The rim is formed of two circular bridges connected by two lateral flanks so as to form a box. The lateral flanks are extended outwardly by two wings, so as to form, with the upper bridge, an annular channel provided to receive a tubular. For certain rims that are provided to receive a tube, the channel is a mere groove formed by a caving-in of the upper bridge. The spokes are connected to the rim by nipples screwed at the end of the spokes. These nipples further make it possible to adjust the tension of the spokes.
To receive the spoke nipples in a conventional manner, the two bridges of the rim are bored with openings spread along the circumference of the rim. The openings of the lower bridge are provided to serve as a seat for the nipple heads. The openings of the upper bridge, with a greater diameter, are provided to enable the positioning of the spoke nipple from the outside.
To improve the conditions in which the nipple head takes support against the rim, and the distribution, in the rim, of the stresses induced by the tension of the spokes, it is known to equip the rims with eyelets that extend through the openings of the lower bridge. These eyelets are assembled by crimping to the periphery of the opening of the lower bridge. They further have a cup-shaped eyelet body whose lower portion rests on the lower bridge, and the upper portion has an edge that rests against the upper bridge. The base of these eyelets is bored for the passage of the nipple body. These eyelets are advantageous because they establish mechanical linkages between the two bridges, which reinforces the structure of the rim and its bending strength.
A monoblock eyelet is described in the patent application Ser. No. EP 130 449. These eyelets also exist in the form of two distinct elements assembled at the level of the crimping.
However, for such rims, the openings of the bridges constitute local weakening zones which weaken each of the two bridges. In addition, these openings must have a relatively large size. The openings of the lower bridge must indeed have a diameter that is sufficient to allow for the passage of the nipple body and its free rotation. The openings of the upper bridge must enable the passage of the nipple head upon which the fastening of the spoke to the rim, as well as the adjustment tools are dependent.
Another problem of these rims is that when adjusting the tension of the spokes, the spoke itself is torsionally biased and twist over itself before a relative movement occurs at the level of the threads for linking with the nipple. As a result, the tension adjustment of the spokes is relatively inaccurate, and the spokes do not work properly.
Another problem of these rims comes from the manufacturing of the eyelets. Indeed, if one wishes to equip the rim with cup-shaped double eyelets, the distance between the two bridges of the rim is directly related to the height of the cup of the eyelet. Since the eyelet is conventionally made of stainless steel by stamping, the maximum height of an eyelet is thereby limited, which imposes dimensional constants for the rim.
However, a rim having threaded openings is known from the published patent application Ser. No. WO 93/09963. The threaded end of the spokes is connected to this rim by means of a nipple that is threaded internally and eternally with a different pitch. This rim further has an unpunched upper bridge, except for the mounting of a valve, if necessary, which makes the rim airtight, and therefore appropriate for the mounting of a tubeless type of tire.
However, the lower bridge that is bored and threaded must be reinforced in its thickness to withstand the stresses, which results in an undesired increase in the weight and inertia of the rim. The mode for mounting the spokes does not solve the spoke twisting problem either.